Chemical fuels release their energy when combined with an oxidizing composition in such a way that a spontaneous chemical reaction occurs. In the case of conventional fuels for land vehicles, the fuel is a hydrocarbon mixture such as gasoline or diesel fuel and the oxidizing composition is air. The fuel burns in the presence of air when initiated by, for example, a spark in an internal combustion engine. For applications requiring higher energy output or thrust, such as rocket or missile propulsion systems, bi-propellant fuel mixtures are generally used. In such bi-propellant mixtures, the fuel and the oxidizer are unstable when mixed together and are generally stored separately.
Bi-propellant rocket propulsion systems consist of oxidizer and fuel propellant tanks, pressurizing system, plumbing, valves, and an engine. A pressurant gas tank or gases from a gas generator pressurize the oxidizer and fuel propellant tanks. When the oxidizer and fuel valves open, the pressurized oxidizer and fuel tanks force the propellants through the plumbing into the engine where the propellants are mixed and ignited. The propellant may be ignited either by ignition aids or by hypergolic chemical reaction. Because ignition aids take up valuable space and weight in the propulsion system, a hypergolic chemical reaction is the preferred ignition method. Certain combinations of fuel and oxidizer are so reactive with one another that they ignite upon contact with one another. The chemical reaction of the fuel and the oxidizer occurs so rapidly that enough heat is generated to continue the combustion reaction in the engine, producing thrust.
Currently known hypergolic bi-propellant rocket propulsion systems have a number of drawbacks. For example, one system consists of monomethylhydrazine and red fuming nitric acid. Because such materials are very toxic, it would be preferred to replace those chemicals in a rocket propulsion system with chemicals less harmful to health. Other commonly used highly toxic storable oxidizers include dinitrogen tetraoxide, mixed oxides of nitrogen, and nitric acid. Commonly used hypergolic fuels used with these oxidizers include hydrazine, monomethylhydrazine and unsymmetrical dimethylhydrazine, all of which are carcinogenic. In U.S. Pat. No. 6,013,143, Thompson has disclosed hypergolic fuel mixtures that contain less-toxic components such as dimethylaminoethylazide (DMAZ). The fuel is hypergolic with inhibited red fuming nitric acid. Although hydrogen peroxide is listed as a possible oxidizer in the Thompson patent, it has been found that the DMAZ fuel by itself is not hypergolic with hydrogen peroxide.
In U.S. Pat. Nos. 5,932,837 and 6,419,771, the Navy has recently created methanol-based fuels that are hypergolic in the presence of highly concentrated hydrogen peroxide (greater than 95%). A shortcoming of using methanol or other low molecular weight alcohols is its low flash point. For example, the flash point of methanol is too low to be considered for some military applications.
It would be desirable to provide bi-propellant systems that avoid the use of toxic and/or dangerous chemicals such as dinitrogen tetraoxide, mixed oxides of nitrogen, nitric acid, hydrazine, monomethylhydrazine and unsymmetrical dimethylhydrazine. Further, it would be desirable to provide hypergolic fuel compositions having a high enough flash point to be useful in military applications.